In the manufacture of printed circuit boards, sheets of copper foil are typically bonded to a dielectric layer of a partially cured epoxy resin containing woven glass fiber (such a dielectric layer is conventionally referred to as a "pre-preg"). In the manufacture of copper clad laminates, sheets of copper foil are typically bonded to another layer of foil. In both processes, the copper foil is etched to produce conductive paths. In such processes, it is extremely important to avoid contamination of the copper foil sheets in that any foreign matter contacting the copper foil, such as resin dust, fiberglass fibers, hair, grease, oil or the like, may result in dots, dents, deposits or pits on the copper foil that can adversely affect the formation of the conductive paths forming the printed circuits.
Copper foil is conventionally formed by an electrodeposition process. Following the production of the copper foil, it is known to secure a metallic substrate to one side of the copper foil to protect that side of the copper foil from contamination during subsequent handling and shipping. The protected side of the copper foil is typically the side used to form the conductive pathways, while the exposed side of the foil is typically the side that is attached to a pre-preg or bonded to another layer of copper foil. The protective metallic substrate remains attached to the copper foil as it is attached to the pre-preg or bonded to the other layer of copper foil. The protective metallic substrate is subsequently removed and discarded (or recycled) to expose the protected, uncontaminated side of the foil for processing to form the conductive pathways.
U.S. Pat. No. 5,153,050 to Johnston discloses a copper/aluminum/copper laminate wherein the shiny side of a copper foil is bonded along its peripheral edges to an aluminum substrate. U.S. Pat. No. 5,674,596 to Johnston further discloses securing copper foil to a metallic substrate, such as a steel or a stainless steel substrate. U.S. Pat. No. 5,512,381 to Konicek et al. discloses securing copper foil to a copper substrate.
Each of the foregoing structures uses a relatively expensive material, e.g., aluminum, stainless steel and copper, to form the disposable, protective substrate. In addition to the cost of such materials, copper and aluminum are relatively soft metals that are susceptible to image transfer during lamination of multi-layer laminates, particularly at high lamination temperatures and pressures. Stainless steel is a stronger metal than copper or aluminum, and possesses the corrosion resistance necessary to avoid contamination of the copper foil sheet. As a result, stainless steel finds advantageous application at higher laminating temperatures and pressures. However, corrosion resistance and higher strength of stainless steel come at a price. Typically, stainless steel sheet is even more expensive than copper and aluminum sheet.
The present invention provides a component for manufacturing printed circuit boards that has a copper foil protected by a metallic substrate, wherein the metallic substrate has the corrosion resistance of stainless steel at a significantly reduced cost.